This invention relates to an optical disk storage system and, more particularly, to a faster, more efficient embedded directory technique for compressing and storing or retrieving data on or from an optical disk to permit rapid data storage and retrieval.
U.S. Pat. No. 5,034,914 discloses an optical disk system which incorporates a new and improved embedded directory technique for storing and retrieving data on or from an optical disk. This technique allows an optical disk storage device to emulate a magnetic media storage device, such as a tape drive, while maintaining plug compatibility with a host computer.
In that patent, a high-level directory is created which relates a file to a number of embedded directories interspersed with data on an optical disk, and written to the disk substantially simultaneously with the data. The embedded directories each provide an index to a number of associated data records, all part of a single corresponding file. The fact that the embedded directories are interspersed with the data reduces the number of long head seeks required to access a particular record. The embedded directories are written onto the disk immediately following the data records to which they correspond. The high-level directory is written onto a predetermined location on the disk, so that it can be located reliably; entries are added to the high-level directory as data is written onto the disk.
The above steps are accomplished by an optical disk controller unit interposed between a host computer and an optical disk storage system. The controller, which includes a microprocessor,
(1) receives data transmitted from the host computer, PA1 (2) generates information for a high-level directory, PA1 (3) constructs embedded directory entries, PA1 (4) controls writing of the record data, and PA1 (5) writes a high-level directory entry, including a table of embedded directory disk addresses, onto the optical disk. PA1 the sequence of records is received at the host interface means and is transferred to the data compression means; PA1 the sequence of records is compressed by the data compression means; PA1 the sequence of compressed records is transferred to the buffer memory means; PA1 the sequence of compressed records is stored in the buffer memory means; PA1 a record directory is created in the buffer memory means; PA1 the record directory is associated with up to a predetermined number of the compressed records; and PA1 the sequence of compressed records and the record directory are stored on the optical media storage device. PA1 copying all of the compressed records associated with the record directory with which the particular record or records sought by the host are associated into the buffer memory means; PA1 employing the record directory to locate the particular compressed record or records sought by the host; PA1 transferring the compressed record or records sought to the data compression means; PA1 decompressing the records or record sought in the data compression means; PA1 transferring the decompressed records from the data compression means to the host interface means; and PA1 transferring the record or records sought to the host from the host interface means.
Relatively speaking, a significant amount of time is required for the optical disk system to store data upon or retrieve data from the optical disk. It is the slowest element of that system, and is the primary source of delay in storing and retrieving data. The greater the amount of data, the greater will be the amount of time required for the optical disk to complete its storage and retrieval tasks. In some cases this may lead to unacceptably slow rates of data storage and retrieval.
Thus, there is a need for an optical media storage device having a faster, more efficient technique for storing and retrieving large amounts of data. The present invention provides one such system to satisfy that need.